Chronic Lymphocytic Leukemia (CLL) is a disease of the white blood cells and is the most common form of leukemia in the Western Hemisphere. CLL represents a diverse group of diseases relating to the growth of malignant lymphocytes that grow slowly but have an extended life span. CLL is classified in various categories that include, for example, B-cell chronic lymphocytic leukemia (B-CLL) of classical and mixed types, B-cell and T-cell prolymphocyic leukemia, hairy cell leukemia, and large granular lymphocytic leukemia.
Of all the different types of CLL, B-CLL accounts for approximately 30 percent of all leukemias. Although it occurs more frequently in individuals over 50 years of age it is increasingly seen in younger people. B-CLL is characterized by accumulation of B-lymphocytes that are morphologically normal but biologically immature, leading to a loss of function. Lymphocytes normally function to fight infection. In B-CLL, however, lymphocytes accumulate in the blood and bone marrow and cause swelling of the lymph nodes. The production of normal bone marrow and blood cells is reduced and patients often experience severe anemia as well as low platelet counts. This can pose the risk of life-threatening bleeding and the development of serious infections because of reduced numbers of white blood cells.
To further understand diseases such as leukemia it is important to have suitable cell lines that can be used as tools for research on their etiology, pathogenesis and biology. Examples of malignant human B-lymphoid cell lines include pre-B acute lymphoblasticleukemia (Reh), diffuse large cell lymphoma (WSU-DLCL2), and Waldenstrom's macroglobulinemia (WSU-WM). Unfortunately, many of the existing cell lines do not represent the clinically most common types of leukemia and lymphoma.
The use of Epstein Barr Virus (EBV) infection in vitro has resulted in some CLL derived cell lines, in particular B-CLL cells lines, that are representative of the malignant cells. The phenotype of these cell lines is different than that of the in vivo tumors and instead the features of B-CLL lines tend to be similar to those of Lymphoblastoid cell lines. Attempts to immortalize B-CLL cells with the aid of EBV infection have had little success. The reasons for this are unclear but it is known that it is not due a lack of EBV receptor expression, binding or uptake. Wells et al. found that B-CLL cells were arrested in the G1/S phase of the cell cycle and that transformation associated EBV DNA was not expressed. This suggests that the interaction of EBV with B-CLL cells is different from that with normal B cells. EBV-transformed CLL cell lines moreover appear to differentiate, possessing a morphology more similar to lymphoblastoid cell lines (LCL) immortalized by EBV.
An EBV-negative CLL cell line, WSU-CLL, has been established previously (Mohammad et al., (1996) Leukemia 10(1):130-7). However, no other such cell lines are known.
There remains a need in the art, therefore, for a CLL cell line which has not been established by transformation with EBV, and which expresses surface markers characteristic of primary CLL cells.